The present application claims priority to Japanese Application No. P11-009831 filed Jan. 18, 1999 and Japanese Application No. P2000-000566 filed Jan. 06, 2000 which applications are incorporated herein by reference to the extent permitted by law.
The present invention relates to a semiconductor device having a bipolar transistor and a process for producing the same, and more particularly to a semiconductor device, in which a (planar) junction type diode is constructed by using impurity regions of a vertical npn bipolar transistor, a horizontal pnp bipolar transistor, and an electrode wiring, and a process for producing the same.
FIG. 1 shows a structure of a semiconductor device of a planar junction type diode using a vertical npn bipolar transistor.
In the semiconductor device having a vertical npn bipolar transistor, an n type high concentration collector buried region (N-BL; N-buried layer) 209 is constructed in a p type semiconductor substrate (P-sub) 206, and an ISO 208 called a channel stopper is constructed in an outer periphery thereof by p type high concentration diffusion in the vertical direction, so that the elements are physically or electrically isolated.
On an upper part of the channel stopper of the p type high concentration impurity region ISO 208, an insulating layer constructed with a silicon oxide film (or an element isolating region, LOCOS; local oxidation of silicon) 207 is further formed. In the region surrounded by the LOCOS 207, elements, such as a transistor, are formed.
On an upper part of the n type high concentration collector buried region 209, an n type epi layer (n type epitaxial layer, or an N-epi layer) 202 is constructed, which is formed by epitaxial growth.
In the n type epitaxial layer 202, a p type intrinsic base region (described as an intrinsic base region or simply as a base region) 201 is constructed. Inside the intrinsic base region 201, an n type high concentration emitter region 203, in which an n type impurity is diffused, is constructed.
Next, on the both ends of the collector buried region 209 to the surface of the epitaxial layer 202, an N+ sinker (PLG; plug) 205 of a high concentration of an n type impurity is constructed to decrease the collector resistance.
Furthermore, over the whole upper surface of the p type semiconductor substrate 206, insulating films 212 and 213 comprising SiO2 are accumulated, with electrode windows for the emitter region 203, base region 201 and N+ sinker 205 constituting a part of collector region being opened, respectively.
On an upper part of the N+ sinker 205 for withdrawing the collector electrode, a metallic electrode film, such as Al, is accumulated along with a base metallic electrode film (sometimes simply referred to as a base electrode) 210 and an emitter metallic electrode film (sometimes simply referred to as an emitter electrode) 214, to constitute a collector metallic electrode film (sometimes simply referred to as a collector electrode) 215. An interlevel insulating film, an upper layer wiring layer are formed on an upper part of the metallic electrode film to constitute an integrated circuit.
As an example using as a circuit where a planar junction type diode is constructed by using the vertical npn bipolar transistor described above, as shown in FIG. 1, a constant bias voltage Vf is applied to the base metallic electrode film 210, the emitter metallic electrode film 214 is made open, and the collector metallic electrode film 215 is connected to the circuit, so as to realize a diode using the base/collector electrodes.
A specific example of an equivalent circuit of the diode constructed by the structure is shown in FIG. 2.
In order to reduce the influence of the parasitic pnp bipolar transistor, as shown in FIG. 1, the P-sub 206 is separated by the collector buried region (N-BL) 209 and the N+ sinker (PLG) 205 of the collector electrode withdrawing region, but it is not sufficient thereby.
The results thereof are shown in FIG. 3. The abscissa is the applied voltage supplied to the base electrode 210 (sometimes referred to as a bias voltage) Vf, which is graduated from 20.5 V to 22.5 V by a step of 0.5 V, and the ordinate indicates the electric current Ic flowing in the collector electrode 215 and the leakage electric current Isub flowing in the P-sub 206, which is graduated in a logarithmic scale in the range of from 0.01 xcexcA to 100 xcexcA.
As shown in FIG. 1 and FIG. 2, however, in the related art planar PN junction type diode using the base/collector junction of the vertical npn bipolar transistor, in the case where the bias voltage is applied to the normal direction, a parasitic pnp bipolar transistor generated between an N-epi layer 202 forming the base region (201) to the collector region of the transistor and the N-BL 209 to the P-sub (206) functions, and thus a leakage electric current (Isub) flowing (leaking) toward the P-sub (206) is generated.
In particular, in the case where trimming with a large electric potential difference between the base region (201) and the P-sub (206) (zapping voltage≅Bvbso) is conducted, the necessary electric current must flow in the normal direction on the Zener zap diode. At this time, a leakage electric current flowing toward the P-sub 206 is generated, and the possibility of forming latch up due to the leakage electric current is increased. The consuming electric power also becomes large as a matter of course.
When the applied voltage Vf supplied to the base electrode of the vertical npn transistor is 21.0 V, the collector electric current Ic is about 1.5 xcexcA, and the leakage electric current Isub is 4.5 xcexcA, i.e., the leakage electric current is larger. When the applied voltage Vf becomes 21.5 V, Ic is 18 xcexcA, and Isub is 30 xcexcA, i.e., Isub is larger. Furthermore, when the applied voltage Vf becomes 22 V, Ic and Isub are substantially the same, which are about 40 xcexcA.
As described herein, in the junction type diode having the structure shown in FIG. 1, the leakage electric current Isub flowing in the P-sub 206 is equivalent to or larger than the electric current Ic flowing in the diode, and thus the leakage electric current is large. That is, the necessary potential difference required for zapping to the Zener zap diode cannot be obtained, and the zapping cannot be certainly conducted. In order to reduce the influence (hFE) of the parasitic pnp transistor, the collector ring structure is employed, as shown in FIG. 1, in which the gap between the p type substrate and the collector is surrounded by the high concentration n+ layer by using the n type buried layer (N-BL) 209 and the collector electric current withdrawing (plug) layer 205, but it cannot be sufficient countermeasure.
The invention relates to a semiconductor device and a process for producing the same, by which the problems associated with the conventional techniques are solved.
A first semiconductor device is equipped with a trimming circuit having a Zener zap diode, the semiconductor device comprising a diode between a terminal for applying a voltage used on trimming the trimming circuit and the Zener zap diode, the diode comprising a first region of a first conductive type and a second region of a second conductive type formed on a substrate, the diode further comprising a third region of the second conductive type in at least a part of the first region, the third region being separated from the second region by the first region, and the third region being connected to the first region with wiring.
The first semiconductor device has a pn junction diode using a base/collector junction of an npn transistor, and by connecting the emitter (the third region) and the base (the first region) by wiring (EB short), the npn transistor is operated in reverse, to increase the collector electric current (Ic). By such a manner, the ratio of Ic becomes large with respect to the leakage electric current (Isub) leaking to the side of the p type substrate. As a result, when the Ic is constant, the leakage electric current (Isub) leaking to the side of the p type substrate is decreased. When the comparison of the ratio Ic/Isub is conducted for the case of emitter-base (EB) open and the case of emitter-base (EB) short by using an npn transistor having a collector ring structure, Ic≅Isub in the case of emitter-base open, whereas Isub is decreased to {fraction (1/7)} to {fraction (1/10)} of Ic in the case of emitter-base short, to exhibit apparent effects.
A second semiconductor device is equipped with a trimming circuit having a Zener zap diode, the semiconductor device comprising a diode between a terminal for applying a voltage used on trimming the trimming circuit and the Zener zap diode, the diode comprising a first region of a first conductive type and a second region of a second conductive type formed on a substrate, the diode further comprising a third region of the second conductive type in at least a part of the first region, the third region being separated from the second region by the first region, the diode further comprising a fourth region of the first conductive type in at least in a part of the second region, the fourth region being separated from the first region by the second region, the third region being connected to the first region with wiring, and the fourth region being connected to the second region with wiring.
The second semiconductor device has a structure combining the first semiconductor device and a third semiconductor device described later, and employs the structure, in which a base 2 (the fourth region) is provided between the base (the first region) and the collector (the second region) of the npn transistor. The collector (the second region) and the base 2 (the fourth region) form a short circuit, and the emitter (the third region) and the base (the first region) also form a short circuit. By such a structure, the Isub (leakage of an electric current to the p type substrate) is suppressed owing to the synergistic effect of the first semiconductor device and the third semiconductor device described later.
A third semiconductor device is equipped with a trimming circuit having a Zener zap diode, the semiconductor device comprising a diode between a terminal for applying a voltage used on trimming the trimming circuit and the Zener zap diode, the diode comprising a first region of a first conductive type formed on a type and a second region of a second conductive type formed in the first region, the diode further comprising a third region of the second conductive type in at least a part of the first region, the third region being separated from the second region and other regions of the second conductive type by the first region, and the third region is connected to the first region with wiring.
The third semiconductor device employs connection of the emitter (the third region) and the base (the first region) of the horizontal pnp transistor, and the collector (the second region) and the base (the first region) are connected (short circuit) with wiring. By such a manner, the Ic can be increased by operating the horizontal pnp transistor, and the ratio of Ic with respect to the leakage electric current (Isub) leaking to the side of the p type substrate is increased. As a result, when the Ic is constant, the amount of Isub is decreased. When the comparison of the ratio Ic/Isub is conducted for the case of collector-base (CB) open and the case of collector-base (CB) short by using the horizontal pnp transistor, Ic≅Isub in the case where the collector-base of the npn transistor is emitter-base open, whereas Isub is decreased to {fraction (1/7)} to {fraction (1/10)} of Ic in the case of collector-base short in the horizontal pnp transistor, to exhibit apparent effects.
In a first process for producing a semiconductor device equipped with a trimming circuit having a Zener zap diode, and comprising a diode between a terminal for applying a voltage used on trimming the trimming circuit and the Zener zap diode, the process comprises a step of forming a buried region of a first conductive type in a semiconductor substrate, a step of forming a semiconductor layer of the first conductive type on the buried region, a step of forming a first region of a second conductive type in the semiconductor layer, a step of forming a second region of the first conductive type in the semiconductor layer, a step of forming a third region of the first conductive type in the first region, and a step of forming an electrode on the first region, the second region and the third region, to commonly connect the electrode on the first region and the third region.
In the first process for producing a semiconductor device, a pn junction diode using a base-collector junction of an npn transistor is formed by connecting the emitter (the third region) and the base (the first region) with wiring (EB short) In the semiconductor device having such a structure formed, the collector electric current (Ic) is increased by operating the npn transistor in reverse (the emitter and the collector are operated in reverse), and thus the ratio of Ic with respect to the leakage electric current (Isub) leaking to the side of the p type substrate is increased. By the process, a semiconductor device can be produced, by which the leakage electric current (Isub) leaking to the side of the p type substrate can be decreased when the Ic is constant.
In the second process for producing a semiconductor device equipped with a trimming circuit having a Zener zap diode, and comprising a diode between a terminal for applying a voltage used on trimming the trimming circuit and the Zener zap diode, the process comprises a step of forming a buried region of a second conductive type in a semiconductor substrate, a step of forming a semiconductor layer of the second conductive type on the buried region, a step of forming a first region of a first conductive type and a fourth region of the first conductive type in the semiconductor layer, a step of forming a second region of the second conductive type on the semiconductor layer, a step of forming a third region of the second conductive type in the first region of the first conductive type, a step of forming an electrode on the first region and the third region, to commonly connect thereto, and a step of forming an electrode on the second region and the fourth region, to commonly connect thereto.
In the second process for producing a semiconductor device, an acceptor region (base 2) (the fourth region) is provided between the base (the first region) and the collector (the second region) of the npn transistor. The collector (the second region) and the base 2 (the fourth region) form a short circuit, and the emitter (the third region) and the base (the first region) form a short circuit, by forming wiring connecting them. By such a structure, the Isub (leakage of an electric current to the p type substrate) is suppressed owing to the synergistic effect of the first semiconductor device and the third semiconductor device described later.
In a third process for producing a semiconductor device equipped with a trimming circuit having a Zener zap diode, and comprising a diode between a terminal for applying a voltage used on trimming the trimming circuit and the Zener zap diode, the process comprises a step of forming a buried region of a second conductive type in a semiconductor substrate, a step of forming a semiconductor layer of the second conductive type on the buried region, a step of forming a first region of a first conductive type and a third region of the first conductive type in the semiconductor layer, a step of forming a second region of the second conductive type connected to the buried region, in the semiconductor layer, a step of forming an electrode on the second region and the third region, to commonly connect thereto, and a step of forming an electrode on the first region.
In the third process for producing a semiconductor device, the emitter (the third region) and the base (the first region) of the horizontal pnp transistor are connected by forming the wiring, and the collector (the second region) and the base (the first region) are connected by forming the wiring, so that they form short circuits, respectively. The Ic can be increased by operating the horizontal pnp transistor formed in this manner, and the ratio of Ic with respect to the leakage electric current (Isub) leaking to the side of the p type substrate can be increased. By the process, a semiconductor device can be produced, by which the leakage electric current (Isub) leaking to the side of the p type substrate can be decreased when the Ic is constant.
Accordingly, the electric current flowing in the diode is increased relative to the leakage electric current to the semiconductor substrate using the npn or pnp bipolar transistor of the invention, whereby the ratio of the leakage electric current to the diode electric current can be improved, it is produced without changing the normal process, and the resistance to latch up due to the leakage electric current can be improved.